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Chapter 14 | Heat and Heat Transfer Methods
14.4 Heat Transfer Methods
17. What are the main methods of heat transfer from the hot core of Earth to its surface? From Earth’s surface to outer space?
When our bodies get too warm, they respond by sweating and increasing blood circulation to the surface to transfer thermal
energy away from the core. What effect will this have on a person in a 40.0ºC hot tub?
Figure 14.30 shows a cut-away drawing of a thermos bottle (also known as a Dewar flask), which is a device designed
specifically to slow down all forms of heat transfer. Explain the functions of the various parts, such as the vacuum, the silvering of
the walls, the thin-walled long glass neck, the rubber support, the air layer, and the stopper.
Figure 14.30 The construction of a thermos bottle is designed to inhibit all methods of heat transfer.
14.5 Conduction
18. Some electric stoves have a flat ceramic surface with heating elements hidden beneath. A pot placed over a heating element
will be heated, while it is safe to touch the surface only a few centimeters away. Why is ceramic, with a conductivity less than that
of a metal but greater than that of a good insulator, an ideal choice for the stove top?
19. Loose-fitting white clothing covering most of the body is ideal for desert dwellers, both in the hot Sun and during cold
evenings. Explain how such clothing is advantageous during both day and night.
Figure 14.31 A jellabiya is worn by many men in Egypt. (credit: Zerida)
14.6 Convection
20. One way to make a fireplace more energy efficient is to have an external air supply for the combustion of its fuel. Another is
to have room air circulate around the outside of the fire box and back into the room. Detail the methods of heat transfer involved
in each.
21. On cold, clear nights horses will sleep under the cover of large trees. How does this help them keep warm?
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